scholarly journals The Gaia DR2 parallax zero-point: hierarchical modelling of red clump stars

2020 ◽  
Vol 493 (3) ◽  
pp. 4367-4381 ◽  
Author(s):  
Victor C Chan ◽  
Jo Bovy
Keyword(s):  
Zero Point ◽  
Absolute Magnitude ◽  
Matched Sample ◽  
Hierarchical Modelling ◽  
Data Release ◽  
Evolution Experiment ◽  
Red Clump ◽  
Photometric Measurements ◽  
Intrinsic Scatter ◽  
Gaia Dr2

ABSTRACT The systematic offset of Gaia parallaxes has been widely reported with Gaia’s second data release, and it is expected to persist in future Gaia data. In order to use Gaia parallaxes to infer distances to high precision, we develop a hierarchical probabilistic model to determine the Gaia parallax zero-point offset along with the calibration of an empirical model for luminosity of red clump stars by combining astrometric and photometric measurements. Using a cross-matched sample of red clump stars from the Apache Point Observatory Galactic Evolution Experiment and Gaia Data Release 2 (DR2), we report the parallax zero-point offset in DR2 to be $\varpi _0 = -48 \pm 1\,\mu \text{as}$. We infer the red clump absolute magnitude to be −1.622 ± 0.004 in Ks, 0.435 ± 0.004 in G, −1.019 ± 0.004 in J, and −1.516 ± 0.004 in H. The intrinsic scatter of the red clump is ∼0.09 mag in J, H, and Ks, or ∼ 0.12 mag in G. We tailor our models to accommodate more complex analyses such as investigating the variations of the parallax zero-point with each source’s observed magnitude, observed colour, and sky position. In particular, we find fluctuations of the zero-point across the sky to be of order or less than a few 10s of $\mu \text{as}$.

scholarly journals Local Stellar Kinematics from RAVE data—VII. Metallicity Gradients from Red Clump Stars

2016 ◽  
Vol 33 ◽  
Author(s):  
Ö. Önal Taş ◽  
S. Bilir ◽  
G. M. Seabroke ◽  
S. Karaali ◽  
S. Ak ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Selection Effects ◽  
Stellar Kinematics ◽  
Experiment Data ◽  
Radial Gradient ◽  
Data Release ◽  
The Difference ◽  
Red Clump

AbstractWe investigate the Milky Way Galaxy’s radial and vertical metallicity gradients using a sample of 47 406 red clump stars from the RAdial Velocity Experiment Data Release 4. Distances are calculated by adopting Ks-band absolute magnitude as −1.54±0.04 mag for the sample. The metallicity gradients are calculated with their current orbital positions (Rgc and Z) and with their orbital properties (Rm and zmax): d[Fe/H]/dRgc = −0.047±0.003 dex kpc−1 for |Z| ≤ 0.5 kpc and d[Fe/H]/dRm = −0.025±0.002 dex kpc−1 for zmax ≤ 0.5 kpc. This reaffirms the radial metallicity gradient in the thin disc but highlights that gradients are sensitive to the selection effects caused by the difference between Rgc and Rm. The radial gradient is flat in the distance interval 0.5-1 kpc from the plane and then becomes positive greater than 1 kpc from the plane. The radial metallicity gradients are also eccentricity dependent. We showed that d[Fe/H]/dRm = −0.089±0.010, −0.073±0.007, −0.053±0.004 and −0.044±0.002 dex kpc−1 for ep ≤ 0.05, ep ≤ 0.07, ep ≤ 0.10 and ep ≤ 0.20 sub-samples, respectively, in the distance interval zmax ≤ 0.5 kpc. Similar trend is found for vertical metallicity gradients. Both the radial and vertical metallicity gradients are found to become shallower as the eccentricity of the sample increases. These findings can be used to constrain different formation scenarios of the thick and thin discs.

scholarly journals The Cepheid period–luminosity–metallicity relation based on Gaia DR2 data

2018 ◽  
Vol 619 ◽  
pp. A8 ◽  
Author(s):  
M. A. T. Groenewegen
Keyword(s):  
Strong Correlation ◽  
Goodness Of Fit ◽  
Zero Point ◽  
Distance Scale ◽  
Distance Modulus ◽  
Initial Sample ◽  
Classical Cepheids ◽  
Data Release ◽  
Multi Mode ◽  
Gaia Dr2

Aims. We use parallax data from the Gaia second data release (GDR2), combined with parallax data based on HIPPARCOS and HST data, to derive the period–luminosity–metallicity (PLZ) relation for Galactic classical cepheids (CCs) in the V, K, and Wesenheit WVK bands. Methods. An initial sample of 452 CCs are extracted from the literature with spectroscopically derived iron abundances. Reddening values, classifications, pulsation periods, and mean V- and K-band magnitudes are taken from the literature. Based on nine CCs with a goodness-of-fit (GOF) statistic smaller than 8 and with an accurate non-Gaia parallax (σπ comparable to that in GDR2), a parallax zero-point offset of −0.049 ± 0.018 mas is derived. Selecting a GOF statistic smaller than 8 removes about 40% of the sample most likely related due to binarity. Excluding first overtone and multi-mode cepheids and applying some other criteria reduces the sample to about 200 stars. Results. The derived PL(Z) relations depend strongly on the parallax zero-point offset. The slope of the PL relation is found to be different from the relations in the LMC at the 3σ level. Fixing the slope to the value found in the LMC leads to a distance modulus (DM) to the LMC of order 18.7 mag, larger than the canonical distance. The canonical DM of around 18.5 mag would require a parallax zero-point offset of order −0.1 mas. Given the strong correlation between zero point, period and metallicity dependence of the PL relation, and the parallax zero-point offset there is no evidence for a metallicity term in the PLZ relation. Conclusions. The GDR2 release does not allow us to improve on the current distance scale based on CCs. The value of and the uncertainty on the parallax zero-point offset leads to uncertainties of order 0.15 mag on the distance scale. The parallax zero-point offset will need to be known at a level of 3 μas or better to have a 0.01 mag or smaller effect on the zero point of the PL relation and the DM to the LMC.

Calibration and characterisation of the Gaia Red Clump

2017 ◽  
Vol 12 (S330) ◽  
pp. 313-316
Author(s):  
L. Ruiz-Dern ◽  
C. Babusiaux ◽  
F. Arenou ◽  
C. Danielski ◽  
C. Turon ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Zero Point ◽  
Absolute Magnitude ◽  
Effective Temperatures ◽  
The Absolute ◽  
Red Clump

AbstractWe present new empirical Colour-Colour and Effective Temperature-Colour Gaia Red Clump calibrations. The selected sample takes into account high photometric quality, good spectrometric metallicity, homogeneous effective temperatures and low interstellar extinctions. From those calibrations we developed a method to derive the absolute magnitude, temperature and extinction of the Gaia RC. We tested our colour and extinction estimates on stars with measured spectroscopic effective temperatures and Diffuse Interstellar Band (DIB) constraints. Within the Gaia Validation team these calibrations are also being used, together with asteroseismic constraints, to check the parallax zero-point with Red Clump stars.

scholarly journals Gaia DR2 giants in the Galactic dust – I. Reddening across the whole dust layer and some properties of the giant clump

2020 ◽  
Vol 500 (2) ◽  
pp. 2590-2606 ◽  
Author(s):  
George A Gontcharov ◽  
Aleksandr V Mosenkov
Keyword(s):  
Absolute Magnitude ◽  
Wide Field ◽  
The Sun ◽  
Theoretical Predictions ◽  
Red Giant Clump ◽  
Red Clump ◽  
Red Giant ◽  
Absolute Magnitudes ◽  
Gaia Dr2 ◽  
Vertical Gradients

ABSTRACT We consider a complete sample of 101 810 giants with Gaia Data Realease 2 (DR2) parallaxes ϖ within the red clump domain of the Hertzsprung–Russell diagram in the space cylinder with a radius of 700 pc around the Sun and a height of |Z| = 1800 pc. We use the Gaia DR2 GBP, GRP, and Wide-field Infrared Survey Explorer W3 photometry. We describe the spatial variations of the modes of the observables GBP − GRP, GRP − W3, $G_\mathrm{BP}+5+5\, \log _{10}\varpi$, $G_\mathrm{RP}+5+5\, \log _{10}\varpi$, and $W3+5+5\, \log _{10}\varpi$ by extinction and reddening in combination with linear vertical gradients of the intrinsic colours and absolute magnitudes of the red giant clump. The derived clump median absolute magnitude in W3 agrees with its recent literature estimates. The clump median intrinsic colours and absolute magnitudes in GBP and GRP are derived for the first time at a precision level of 0.01 mag. We confirm the reliability of the derived clump absolute magnitudes, intrinsic colours, and their vertical gradients by comparing them with the theoretical predictions from the PAdova and TRieste Stellar Evolution Code, MESA Isochrones and Stellar Tracks, and Bag of Stellar Tracks and Isochrones. This leads us to the median age and [Fe/H] of the clump within |Z| < 1.7 kpc from the Galactic mid-plane as $(2.3\pm 0.5)+(3.2\pm 1.6)\, |Z|$ Gyr and $(-0.08\pm 0.08)-(0.16\pm 0.07)\, |Z|$ dex, respectively, where Z is expressed in kpc. These results agree with recent empirical and theoretical estimates. Moreover, all the models give similar age–metallicity relations by use of our results in the optical range. The derived extinctions and reddenings across the whole dust half-layer below or above the Sun converge to the reddening E(B − V) = 0.06 mag by use of the most reliable extinction laws.

scholarly journals The Parallax Zero-point of Gaia Early Data Release 3 from LAMOST Primary Red Clump Stars

2021 ◽  
Vol 910 (1) ◽  
pp. L5
Author(s):  
Yang Huang ◽  
Haibo Yuan ◽  
Timothy C. Beers ◽  
Huawei Zhang
Keyword(s):  
Zero Point ◽  
Early Data ◽  
Data Release ◽  
Red Clump

scholarly journals New light on the Gaia DR2 parallax zero-point: influence of the asteroseismic approach, in and beyond the Kepler field

2019 ◽  
Vol 628 ◽  
pp. A35 ◽  
Author(s):  
S. Khan ◽  
A. Miglio ◽  
B. Mosser ◽  
F. Arenou ◽  
K. Belkacem ◽  
...  
Keyword(s):  
Zero Point ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Scaling Relations ◽  
Red Giants ◽  
The Third ◽  
Red Clump ◽  
Red Giant ◽  
Gaia Dr2 ◽  
Efficient Elimination

The importance of studying the Gaia DR2 parallax zero-point by external means was underlined by the articles that accompanied the release, and initiated by several works making use of Cepheids, eclipsing binaries, and asteroseismology. Despite a very efficient elimination of basic-angle variations, a small fluctuation remains and shows up as a small offset in the Gaia DR2 parallaxes. By combining astrometric, asteroseismic, spectroscopic, and photometric constraints, we undertake a new analysis of the Gaia parallax offset for nearly 3000 red-giant branch (RGB) and 2200 red clump (RC) stars observed by Kepler, as well as about 500 and 700 red giants (all either in the RGB or RC phase) selected by the K2 Galactic Archaeology Program in campaigns 3 and 6. Engaging in a thorough comparison of the astrometric and asteroseismic parallaxes, we are able to highlight the influence of the asteroseismic method, and measure parallax offsets in the Kepler field that are compatible with independent estimates from literature and open clusters. Moreover, adding the K2 fields to our investigation allows us to retrieve a clear illustration of the positional dependence of the zero-point, in general agreement with the information provided by quasars. Lastly, we initiate a two-step methodology to make progress in the simultaneous calibration of the asteroseismic scaling relations and of the Gaia DR2 parallax offset, which will greatly benefit from the gain in precision with the third data release of Gaia.

scholarly journals Empirical photometric calibration of the Gaia red clump: Colours, effective temperature, and absolute magnitude

2018 ◽  
Vol 609 ◽  
pp. A116 ◽  
Author(s):  
L. Ruiz-Dern ◽  
C. Babusiaux ◽  
F. Arenou ◽  
C. Turon ◽  
R. Lallement
Keyword(s):  
Effective Temperature ◽  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Red Giants ◽  
Photometric Calibration ◽  
Empirical Calibration ◽  
Data Release ◽  
Red Clump ◽  
Red Giant ◽  
Absolute Magnitudes

Context. Gaia Data Release 1 allows the recalibration of standard candles such as the red clump stars. To use those stars, they first need to be accurately characterised. In particular, colours are needed to derive interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. Aims. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia red clump stars of the solar neighbourhood through colour–colour, effective temperature–colour, and absolute magnitude–colour relations from the Gaia, Johnson, 2MASS, Hipparcos, Tycho-2, APASS-SLOAN, and WISE photometric systems, and the APOGEE DR13 spectroscopic temperatures. Methods. We used a 3D extinction map to select low reddening red giants. To calibrate the colour–colour and the effective temperature–colour relations, we developed a MCMC method that accounts for all variable uncertainties and selects the best model for each photometric relation. We estimated the red clump absolute magnitude through the mode of a kernel-based distribution function. Results. We provide 20 colour versus G−Ks relations and the first Teff versus G−Ks calibration. We obtained the red clump absolute magnitudes for 15 photometric bands with, in particular, MKs = (−1.606 ± 0.009) and MG = (0.495 ± 0.009) + (1.121 ± 0.128)(G−Ks−2.1). We present a dereddened Gaia-TGAS HR diagram and use the calibrations to compare its red clump and its red giant branch bump with Padova isochrones.

scholarly journals Inferring the parallax of Westerlund 1 from Gaia DR2

2019 ◽  
Vol 492 (2) ◽  
pp. 2497-2509 ◽  
Author(s):  
Mojgan Aghakhanloo ◽  
Jeremiah W Murphy ◽  
Nathan Smith ◽  
John Parejko ◽  
Mariangelly Díaz-Rodríguez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Bayesian Model ◽  
Main Sequence ◽  
Zero Point ◽  
Star Cluster ◽  
Initial Mass ◽  
Data Release ◽  
The Galaxy ◽  
Late Stages ◽  
Gaia Dr2

ABSTRACT Westerlund 1 (Wd1) is potentially the largest star cluster in the Galaxy. That designation critically depends upon the distance to the cluster, yet the cluster is highly obscured, making luminosity-based distance estimates difficult. Using Gaia Data Release 2 (DR2) parallaxes and Bayesian inference, we infer a parallax of $0.35^{+0.07}_{-0.06}$ mas corresponding to a distance of $2.6^{+0.6}_{-0.4}$ kpc. To leverage the combined statistics of all stars in the direction of Wd1, we derive the Bayesian model for a cluster of stars hidden among Galactic field stars; this model includes the parallax zero-point. Previous estimates for the distance to Wd1 ranged from 1.0 to 5.5 kpc, although values around 5 kpc have usually been adopted. The Gaia DR2 parallaxes reduce the uncertainty from a factor of 3 to 18 per cent and rules out the most often quoted value of 5 kpc with 99 per cent confidence. This new distance allows for more accurate mass and age determinations for the stars in Wd1. For example, the previously inferred initial mass at the main-sequence turn-off was around 40 M⊙; the new Gaia DR2 distance shifts this down to about 22 M⊙. This has important implications for our understanding of the late stages of stellar evolution, including the initial mass of the magnetar and the LBV in Wd1. Similarly, the new distance suggests that the total cluster mass is about four times lower than previously calculated.

scholarly journals The SAMI Galaxy Survey: stellar population and structural trends across the Fundamental Plane

2021 ◽  
Author(s):  
Francesco D’Eugenio ◽  
Matthew Colless ◽  
Nicholas Scott ◽  
Arjen van der Wel ◽  
Roger L Davies ◽  
...  
Keyword(s):  
Stellar Population ◽  
Mass Density ◽  
Empirical Relation ◽  
Zero Point ◽  
High Signal ◽  
Fundamental Plane ◽  
Surface Mass ◽  
Integral Field Spectroscopy ◽  
Surface Mass Density ◽  
Photometric Measurements

Abstract We study the Fundamental Plane (FP) for a volume- and luminosity-limited sample of 560 early-type galaxies from the SAMI survey. Using r −band sizes and luminosities from new Multi-Gaussian Expansion (MGE) photometric measurements, and treating luminosity as the dependent variable, the FP has coefficients a = 1.294 ± 0.039, b = 0.912 ± 0.025, and zero-point c = 7.067 ± 0.078. We leverage the high signal-to-noise of SAMI integral field spectroscopy, to determine how structural and stellar-population observables affect the scatter about the FP. The FP residuals correlate most strongly (8σ significance) with luminosity-weighted simple-stellar-population (SSP) age. In contrast, the structural observables surface mass density, rotation-to-dispersion ratio, Sérsic index and projected shape all show little or no significant correlation. We connect the FP residuals to the empirical relation between age (or stellar mass-to-light ratio ϒ⋆ ) and surface mass density, the best predictor of SSP age amongst parameters based on FP observables. We show that the FP residuals (anti-)correlate with the residuals of the relation between surface density and ϒ⋆ . This correlation implies that part of the FP scatter is due to the broad age and ϒ⋆ distribution at any given surface mass density. Using virial mass and ϒ⋆ we construct a simulated FP and compare it to the observed FP. We find that, while the empirical relations between observed stellar population relations and FP observables are responsible for most (75 per cent) of the FP scatter, on their own they do not explain the observed tilt of the FP away from the virial plane.

scholarly journals Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars

2016 ◽  
Vol 11 (S321) ◽  
pp. 50-50
Author(s):  
Daisuke Toyouchi ◽  
Masashi Chiba
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Radial Velocities ◽  
Galactocentric Distance ◽  
Chemical Abundances ◽  
Structure And Dynamics ◽  
Evolution Experiment ◽  
Dynamical Properties ◽  
Red Clump ◽  
Independent Work

AbstractWe investigate the structure and dynamics of the Milky Way (MW) disk stars based on the analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data, to infer the past evolution histories of the MW disk component(s) possibly affected by radial migration and/or satellite accretions. APOGEE is the first near-infrared spectroscopic survey for a large number of the MW disk stars, providing their radial velocities and chemical abundances without significant dust extinction effects. We here adopt red-clump (RC) stars (Bovy et al. 2014), for which the distances from the Sun are determined precisely, and analyze their radial velocities and chemical abundances in the MW disk regions covering from the Galactocentric distance, R, of 5 kpc to 14 kpc. We investigate their dynamical properties, such as mean rotational velocities, 〈Vφ〉 and velocity dispersions, as a function of R, based on the MCMC Bayesian method. We find that at all radii, the dynamics of alpha-poor stars, which are candidates of young disk stars, is much different from that of alpha-rich stars, which are candidates of old disk stars. We find that our Jeans analysis for our sample stars reveals characteristic spatial and dynamical properties of the MW disk, which are generally in agreement with the recent independent work by Bovy et al. (2015) but with a different method from ours.

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